Counterbalancing apparatus



Nov. 26, 1968 Jlw. BINNS COUNTERBALANCING APPARATUS 2 Sheets-Sheet 1Filed Feb. 2, 1967 INVENTOR. JO/M/ l1! E/IV/VS BY MM 2 Sheets-Sheet 2Filed Feb. 2, 1967 mvsm'on. dol/n/ 11/. 5/4/46 A "pe d 6X8 United StatesPatent 3,412,423 COUNTERBALANCING APPARATUS John W. Binns, ClaridonTownship, Marion County, Ohio, assignor to Overhead Door Corporation,Dallas, Tex., a corporation of Indiana Filed Feb. 2, 1967, Ser. No.613,534 8 Claims. (Cl. 16-198) ABSTRACT OF THE DISCLOSURE Acounerbalancing mechanism for an upwardly acting door is secured to theframe around a door opening and comprises a pair of coaxial shaftsrotatably supported at the ends thereof upon the door frame of a truck,for example, near the upper edge of the opening. Each of the shaftssupports a cable drum which is securely fastened thereto, and the cablesare connected between said drums and the lower end of said door. Thecounterbalancing mechanism is provided with coupling meansinterconnecting said shafts and permitting a limited amount of relativerotation of said shafts. Tension means connected between said shafts andsaid door urges said shafts to wind the cables on the drums.

Background of the invention This invention relates in general to acounterbalancing mechanism for an upwardly operated door mounted in therear end of a truck van and, more particularly, to a type thereof havinga pair of spring-actuated coaxial cable drums having cables connected tosaid door and coupled together so that the door can be operated withsome counterbalancing effect when one of the springs or one of thecables fails.

Known counterbalancing mechanism for upwardly operated doors comprises apair of shafts on which are secured a pair of counterbalancing cabledrums. The shafts are preloaded by a pair of torsion springs tocounterbalance the weight of the door, such as a truck door, to whichthe cables are attached. Thus, when the door is closed, it may beraised, hence opened, relatively easily due to the fact that much of itsweight is counteracted by the torques of the torsion springs. Likewise,the door can be closed at an easily regulatable rate, thereby preventingthe door from slamming shut, by applying a relatively small amount ofmanual force.

This system, however, has several disadvantages which impair thedesirability of its use. For example, if one of the cables breaks, itimmediately releases the tension or torque on its associated springwhich then unwinds rapidly, and usually with sufficient force to damagethe spring or its mounting. Thereafter, the door is balanced with onlyone spring and the remaining cable, which provides only half of theoriginal support. However, by coupling the drums (or shafts) together,both springs operate through the single cable to support the door in asubstantially conventional manner until the defective cable can berepaired or replaced.

With an existing counterbalance system having a broken cable, asdescribed in the preceding paragraph, failure of the spring connected tothe operative cable will completely immobilize the system. However, ifthe shafts are coupled, the s ring associated with the damaged cablewill still act through the good cable to provide about 50 percent of thenormal support. In fact, this further safety factor is providedregardless of which spring or which cable should fail.

It follows from the foregoing that failure of one spring will reduce thesupport of the counterbalance mechanism by about 50 percent, but bothcables will be kept taut, hence away from interference with the normaloperation ice of the door. With existing systems, the cable connected tothe damaged spring will hang loose in or near the door opening where itcan interfere with loading operations and with the movement of the door.

It is difficult to ensure constant and uniform performance between thetwo, coupled units of a counterbalance system, which are rigidlyinterlocked for simultaneous rotation, due to variations in springtorque, cable stretch, frame alignment, friction and the like. Thus, itis essential in this system to provide a shaft coupling mechanism whichperimts limited relative rotational movement between the shafts (ordrums). Moreover, a pair of coupled, but relatively rotatable, shafts asproposed provides cable movement control during the winding andunwinding movement which has not been possible with uncoupled shafts oreven with a single shaft for both drums.

Accordingly, the objects of this invention are:

(1) To provide a counterbalancing mechanism including a pair ofcable-supporting drums which are connected to independent spring meansand which are coupled for limited rotation whereby one cable and/or onespring can fail without completely immobilizing the system.

(2) To provide a door counterbalancing mechanism, as aforesaid, whichdoes not depend on an accurate door installation for proper operation.

(3) To provide a door counterbalancing mechanism, as aforesaid, whereinthe door may be tied down upon an irregular load without permitting thecable on the cable drums to jump off the cable drums due to the shockson the door caused by the vehicle moving over rough roads.

(4) To provide a counterbalancing mechanism, as aforesaid, which is easyto assemble and install.

Other objects and purposes of this invention will become apparent topersons acquainted with apparatus of this general type upon reading thefollowing specification and inspecting the accompanying drawings, inwhich:

FIGURE 1 is a perspective view of the rear end of a truck enclosure anddoor structure embodying the invention.

FIGURE 2 is a broken, side elevational view of the counterbalancingmechanism embodying the invention.

FIGURE 3 is a sectional view taken on the line III-III in FIGURE 2.

FIGURE 4 is a sectional view taken on the line IVIV in FIGURE 3.

FIGURE 5 is a sectional view similar to FIGURE 3 with the pin rotated toone of its extreme limits.

Certain terminology will be used in the following description forconvenience in reference only and will not be limiting. For example, thewords upwardly, downwardly, rightwarclly and leftwardly will designatedirections in the drawings to which reference is made. The wordsinwardly and outwardly will refer to directions toward and away from,respectively, the geometric center of the device and designated partsthereof. Said terminology will include the words above specificallymentioned, derivatives thereof and words of similar import.

Description A counterbalancing mechanism 10 for an upwardly acting door16 is illustrated in FIGURE 1 for use with a truck 11 having a van orclosed compartment 12 having a door opening 13 at its rear end. The door16 is supported for movement along rails, one of which is shown at 14,mounted to the frame along said door opening. More particularly, andreferring to FIGURE 2, the counterbalancing mechanism 10 comprises twoshafts 17 and 18 independently and rotatably sup ported on thecompartment frame 19 around and above the door opening 13 by brackets21, 22, 23, 24 and 25.

The bracket 21 is generally L-shaped and has its leg 27 (FIGURE 2)secured to the frame 19 by a plurality of bolts 28. The other leg 29 ofthe bracket 21 has an opening therethrough for the reception of theouter end of shaft 17. A bearing 31 is secured to the leg 29 by bolts32, and the shaft 17 is rotatable therewithin.

The bracket 22 is generally L-shaped having a leg 42 secured to saidframe 19 by the bolts 34 and a leg 43 extending perpendicularly awaytherefrom. The inner end i of the shaft 17 is rotatably supported by thebearing 33 which is secured to the leg 43 by bolts 41. Mounted coaxiallyon the shaft 17 and extending leftwardly from the bracket 22 is a cabletensioning torsion spring 38 having its left end secured to the shaft 17by a lock collar having a set screw 39 and having its right end securedto the leg 43 of the bracket 22 by the bearing 33.

Adjacent the bracket 21, a cable drum 34 is securely fastened to theshaft 17 by a set screw 36. The cable drum 34 is provided with a cable37 wrapped therearound and preferably fastened at its free end to thelower edge of the door 16.

The bracket 24 is generally L-shaped and has a leg 46 secured to theframe 19 by a plurality of bolts 47, of which one is shown in FIGURE 2.The other leg 48 of the bracket 24 extends perpendicularly to the axisof the shaft 18. The leg 48 has an opening therethrough for thereception of the outer end of the shaft 1 8, and a bearing 49 is securedto the leg 48 by bolts 51, so that the shaft 18 is rotatabletherewithin.

The shaft 18 supports a cable drum 53 which is securely fastened theretoby a set screw 54 and rotatable therewith. The cable drum 53 is providedwith a cable 55 wrapped therearound and fastened at its free end to thelower edge of the door 16.

An intermediate bracket 25 is secured to the frame 19 between thebrackets 23 and 24. Bracket 25 is preferably L-shaped having a leg 57secured to the frame 19 by a plurality of bolts 56, and a leg 59extending away there- 'from perpendicular to the axis of the shaft 18. Acable tensioning torsion spring 45 extends inwardly away from the leg 59of the bracket 25 and is preferably identical to the torsion spring 38on the shaft 17. The torsion spring 45 is secured to the leg 59 by thebearing 60 which sup ports the shaft 18 and is secured to the leg 59 bythe bolts 61. The inner end of the torsion spring 45 is secured to theshaft 18 by a lock collar 50 having a set screw 62.

The leg 44 of the bracket 23 has attached thereto a bearing 63 throughwhich the inner end of the shaft 18 is received and is rotatablysupported. The bearing is secured to the leg 44 by bolts 64.

In this embodiment, the shafts 17 and 18 are shown as coaxial, abuttingand connected together by a coupling 66 (FIGURE 4).

The coupling 66 comprises a cylindrical sleeve 68 having a coaxialopening 67 extending therethrough. The diameter of the opening 67 at theleft end of the sleeve 68 is of the same diameter as the shaft 17.However, said opening has a portion 70 of enlarged diameter at the rightend of the sleeve 68 which is of a diameter greater than the diameter ofthe shaft 18.

The sleeve 68 (FIGURE 4) is rigidly secured to the shaft 17 by means ofa pin 71 extending through diametrical openings provided in the sleeve68 and the shaft 17. The inner end of the shaft 18 extends into theopening 70 in the right end of the sleeve 68 to a point adjacent, butaxially spaced from, the inner end of the shaft 17. The rightward end ofthe sleeve 68 (FIGURES 3 and 4) is provided with a pair of diametricallyopposed, circumferentially aligned and extending slots 73 and 74separated by abutments 75 and 76. A pin 72 extends diametrically throughthe shaft 18 so that its opposite ends extend into the slots 73 and 74,respectively, of the sleeve 68. The pin 72 is arranged so that itengages the corresponding, circumferential sides of the abutmentssimultaneously.

The shaft 18 and sleeve 68 have diametrically aligned openings 81 and 82disposed between the shaft 17 and 4 pin 72 through which the shank of aneyebolt 83 is slide ably received for holding said shafts 17 and 18,hence the drums 34 and 53 against relative rotation. The openings 81 and82 are aligned when the pin 72 is centered between the abutments 75 and76.

Operation Although the operation of the device embodying the inventionhas been indicated above, said operation will be detailed hereinbelow toassure a more complete understanding of the invention.

The counterbalancing mechanism 10 is installed, upon the frame 19 of thevan 12 with the eyebolt 83 in the openings 81 and 82. The cables 37 and55 are connected to a door 16 and the torsion springs 38 and 45 areproperly adjusted so that the weight of the door is properly balanced.The eyebolt 83 is then removed so that the shafts 17 and 18 can rotaterelatively within the limits imposed by the pin 72 and abutments 75 and76. That is, the amount of relative rotation of the shafts 17 and 18 ineither direction is stopped when the pin 72 comes in contact with theabutments 75 and 76.

The slots 73, 74 and abutments 75, 76 are circumferentially arranged sothat the opposite ends of the pin 72 will contact the abutments 75 and76 simultaneously. Thus, the shearing force on the pin will bedistributed equally on both ends of pin 72 and both abutments.Variations in the performance of the two parts of the mechanism 10, suchas the tension applied to cables 37 and 55, will be compensated for bythe coupling 66. That is, the sleeve 68 is able to rotate with respectto the shaft 18 to compensate for differences in tension upon the cable37 and cable 55. Moreover, if one cable or one spring should break orfail, the other cable or spring will automatically take over, due to thecoupling 66. In fact, the counterbalance mechanism will continue toperform at about 50 percent effectiveness even with either cable andeither spring disabled.

Although a particular prefered embodiment of the invention has beendisclosed above for illustrative purposes, it will be understood thatvariations or modifications thereof, which lie within the scope of theappended claims, are fully contemplated.

The embodiments of the invention in which an exclusive property orprivilege is claimed are defined as follows:

1. A mechanism secured to the frame around a door opening forcounterbalancing the weight of an upwardly acting door mounted adjacentsaid opening, comprising:

a pair of relatively rotatable shafts rotatably supported upon said doorframe near the upper end of said opening;

a cable drum securely fastened to each shaft and having a cable woundthereon and fastened to said door; means interconnecting said shafts forlimiting the relative rotation of said shafts; and

torque means connected between said shafts and said frame for opposingrotation thereof in a direction for unwinding said cables from saiddrums.

2. The device defined in claim 1, wherein said shafts are coaxial andabutting.

3. The device defined in claim 2, wherein said means interconnectingsaid shafts comprises first stop means secured to one of said shafts andsecond stop means secured to the other of said shafts, said first andsecond stop means being adapted to engage each other to limit therelative rotation of said shafts.

4. The device defined in claim 3, wherein said first stop meanscomprises a sleeve secured to one of said shafts, said sleeve having apair of circumferentially spaced and circumferentially extending slots;and

wherein said second stop means comprises a pair of projections extendingradially outwardly from the other of said shafts and extending into saidslots, said projections being adapted to simultaneously engage thecorresponding ends of said slots to limit the amount of relativerotation of said shafts.

5. The device defined in claim 4, wherein said other shaft extends intosaid sleeve and they have diametrically aligned openings which arealigned when said projections are disposed midway between the ends ofsaid slots; and

bolt means adapted for removable insertion into said diametricallyaligned openings for holding said shafts against relative rotation.

6. The device defined in claim 4, wherein said pair of radiallyextending projections comprise the opposite ends of a pin extendingdiametrically through said other of said shafts, and said slots arediametrically disposed and of equal length.

7. The device defined in claim 4, wherein one end of said other shaft isin a telescoped relation with said sleeve.

8. The device defined in claim 7, wherein said other shaft is receivedinto an opening in one end of said sleeve and said projections extendoutwardly through said slots.

References Cited UNITED STATES PATENTS BOBBY R. GAY, Primary Examiner.

I. L. KOHNEN, Assistant Examiner.

